Laurel Canyon

Supria Rosner


Are you obsessed with crime shows like CSI? Well, life as a forensic scientist isn’t quite like it appears on TV—it’s better. We talk to DNA Technical Lead Supria Rosner about life in the LAPD, her role in solving a 20-year murder mystery, and the importance of always trying.


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You grew up here in LA, but left for a while. How did you end up back here?
I did my undergrad at Berkeley to study science. Everybody was really interested in me being a doctor, but I always thought about forensics back when I was little. Actually, I saw this movie when I was eight or nine called Feds with Rebecca De Mornay, about women FBI agents. I've always liked science and math, so I thought, "Okay, this would be one way to merge them."

Back then, there was no [TV series] CSI or anything. When I graduated high school in '96 and went to college, there were only a few schools with forensics programs at the time. One of the forensic schools started in Berkeley, but it shut down. A lot of the former students went on to create new schools—one of them was Dr. Peter De Forest, who started a program at John Jay College of Criminal Justice in New York.

When I was an undergrad, I was like, "Oh, I'll never be able to go to New York." I grew up in California, and New York was always so far for me. But it just so happened that my sister moved out there to become a legal-aid attorney, and she said, "Oh, my roommate left; do you want to move here?" and I said, "Okay, I'm there."

Then my acceptance into the program was delayed. My professor had gone to Berkeley, so I kind of gave him a sob story. I said, “Please, I've been wanting to do this since I was seven; I don't want to wait a year!" So then, he said that they’d accept me on a preliminary basis and see how I did.

That's amazing!
Yeah, but the program was very small. I graduated college in 2000. There wasn’t a lot of exposure about DNA testing other than the O. J. Simpson case, which kind of introduced the world to DNA testing.

When I graduated, I got a job at the Office of Chief Medical Examiner, the OCME. They had a forensic lab that just did DNA, and that's where I first started.

Always keep trying. Stuff will always work out.

Why DNA?
I think because my background was biology. There are a lot of different forensic disciplines; I did an internship at the NYPD where they did a lot of drug chemistry and things like that, but I always had an interest in DNA.

I was a DNA analyst at the OCME, so I was analyzing homicides, property crimes, sexual-assault kits for biological fluids. What was big about New York is that the city did most of the World Trade Center victim identifications. I started at the OCME in '04 but we were still doing identifications from 2001.

They spent years and years going over the 20,000 fragments that were found at the site. Some pieces are smaller than the tip of a thumb. It's a huge project and it's still ongoing. When I was there, they had created a sifting facility because they realized that all the dirt that they removed right away still had some fragments in it, and so they sifted through all of that dirt.

Cases like that are difficult because when there’s a lot of heat, there’s not a lot of DNA left. So you often have to do other types of testing to see if you can identify it.

There are four steps to the DNA process. The first step is extracting the DNA, getting it out of those cells and then cleaning it up. The second step is telling you how much DNA you have; you need that to optimize the further steps to generate a DNA profile.

Ninety-nine percent of our DNA is all the same; it's just a small percentage that's different. Our DNA is filled with these repetitive units—it's the number of these repeats that's different between person to person, and that's what we look for, forensically, with DNA testing. If you see a DNA profile, it looks like a string of numbers, and we look at locations on the chromosomes. You can kind of think of them like addresses on the chromosome. You have two numbers, one from your mom, one from your dad—that number represents the number of repeats, or that repetitive unit in your DNA, so that's why you get this string of numbers.

If I say that at this one location I'm an 11-12, that means I have 11 repeats on one chromosome from one parent and 12 from the other. Then, I obtain a DNA profile from blood or biological fluid from a crime scene, and compare it to a known person to either include or exclude.

So, there’s a giant database of DNA profiles that you can search?
There's an FBI database that houses a group of known individuals, mostly convicted offenders. The database has different sections: one is unknowns from DNA profiles, another one is convicted offenders or known individuals, and the third is a missing person's database.

There are a lot of rules for what can be compared. But let's say your car gets burglarized and the suspect just happens to leave a cup behind. We would be able to swab it, type it, generate a DNA profile, upload it to the database, and see if there are any potential hits.

What about when you’re looking for someone who doesn't have their DNA recorded anywhere?
Yeah, so sometimes those are cases that are unsolved. An investigator could say, "I have an idea for who it is, so let me get you a reference sample from that person so you can do a comparison." Not everybody's in the database, so then we can do a case-to-case comparison, or sometimes we obtain a profile. The system is always being updated with new profiles.

California became an “all-arrestee” state, which means if you're arrested for a felony or a misdemeanor, you have to provide a DNA sample that goes in the database. Not all states are like that, though more of them are moving towards that. And then, if you're not in the database, there's something called a familial database search.

There was a really big case that I worked on called the “Grim Sleeper, which was a serial pattern of homicides dating back to the '80s. Over 20 years, there was always this DNA profile that was found on every victim’s body. He was called the Grim Sleeper, because he “slept” in between the murders; there'd be six or seven years of no killings in between.

We always had the DNA profile but no match. Eight or nine years ago, the police still didn't know who the killer was, so they created a task force to see if any work could be done. So finally, the Department of Justice and the police department worked out a way to search the database for not just a specific person, but for a relative of that person. This was very controversial at the time—because if you see DNA that's somewhat related, it might not be from an actual relative, it might just be a fortuitous match. You have to do your investigations to figure out. California was one of the first states to do it.

In 2007, they decided to run a database search to see if they could find any relatives of the killer.  Sure enough, they found a relative in the database; it turned out to be the Grim Sleeper's son, who was arrested for a felony weapons possession.

Now they investigate: Does the son have any relatives that could be the suspect? The investigation pinpointed this one person, so they started following him. After a few days of not leaving his house, he went to a pizza party in Orange County, so our surveillance unit followed him and pretended to be a busboy. They collected this guy’s pizza leftovers and brought them into the office, and that's what I got.


It's like in the movies! [Laughs]
Yeah! Sure enough, the DNA on the pizza slice matched all these DNA profiles and he was arrested. We tried and testified in this case just last year.

You testified?
Yeah, I testified for the DNA results that the LAPD did on the case. He was charged with ten homicides and one attempt, and was found guilty.

What is your role in a given case?
So, we get a synopsis, like a case narrative of what happened. The DNA analyst has to know a little bit about the case, so that you know what you're looking for. What type of biological fluid, whether it's touch DNA, semen, blood, or saliva. You have to know if there are multiple people involved, so you can look for three possible people, or two, or one.

You analyze the case, you look at the evidence, you get a result and you write a report. But because we work for the police on very complicated cases, we offer a consultation for the investigator—we review the murder books, we look at photographs, and we can give advice to the investigator about what to analyze. Sometimes it's hard to determine how to test an item of evidence: "Do I do prints on it? Do I do DNA to see who handled it? What's the best order of business?" So, on those kinds of things, the detectives ask us. It's usually homicides or complicated sexual assaults where the detectives really need a scientist to look at all the evidence and determine what's the best thing to test.

Are you assigned to a case and then Friday afternoon comes around and you're like, "Okay, I'm off for the weekend and I'll just pick this up on Monday." Is that how it works?
[Laughs] These TV shows make you think we just type something in and then a picture of the person comes up and we say, "Oh, arrest him!" You're right, it does not work like that. Everything's ongoing. It's not a process that one person can take on from beginning to end. Because we get so much work and so many cases, we really have to work in a team. I almost think of it like a car-assembly line. There are always samples and always cases to be worked on.

So, in a typical week, you could be screening the evidence on the first day, and doing DNA extraction on the second day, and interpreting the DNA profiles on the fourth day, and then writing the reports. What takes a long time is the interpretation of the results. The instrument generates almost like a graph with a series of peaks. A DNA analyst is trained to read those. What's getting more complicated in our field are mixtures—that's where it takes a little bit of experience to understand, to see if there's information that you can pull out of it.

What do you mean by “mixtures?”
Let's say there was a blood stain and somebody spit on the blood stain. You would obtain a profile with a bunch of different numbers, one belonging to the blood donor, one from the saliva donor. So, if they're in different quantities, a DNA analyst like myself is able to determine a major profile or a minor profile, if one is in excess of another one.

And that's just with biological fluids. Our testing is getting so sensitive that we're doing a lot of touch DNA analysis, like if a person was hit by bat. We'll swab the bat and get a mixture of three or four individuals, because many people have touched it. As an analyst, we interpret that, to see if there's any information we could get from it.

Wow. How do you sleep at night? [Laughs]
I think our jobs are very removed from the crimes, because it's all on paper. You read the story, you see the bloody clothes, and things like that.  The hardest part is a trial when you see the defendant. Our job is to explain the science to the jury, but that's really the first time that you actually see the parties involved.

So, you don't get freaked out?
I don't really. Sometimes it's just wrong place, wrong time, you know? You get a lot of drive-by shootings or things like this that you can't control. I think what's difficult for me, especially now I have a baby, is the crimes against children and the sexual assaults.

I feel like there must be disturbing stuff happening all the time.
Yeah, there is. But at least in LA, the Los Angeles Police Department is a very big organization. I like feeling protected, and knowing that we have the technology and the resources to help. And we're only getting better and better. When I first started, we primarily looked at homicides and sexual assaults; we had a limited resources, so we worked on the violent crimes to solve those first. But more and more, we're doing property crimes and things like that.


Where do you see yourself in five years, or ten years?
I love the LAPD and I love the laboratory, so I definitely see myself still there. I hope that I could just continue managing. Now I'm a supervisor, but there's an assistant lab director, and then you can become the laboratory director and then the highest civilian position you can have is commanding officer of the laboratory and the police department. After that you need to be sworn. I just really see myself continuing as far as I can go. I don't want to move away from the science, though.

What’s the best piece of advice you would give?
Always keep trying. Stuff will always work out.

What about advice for a career in forensic science?
Don't trust the TV shows to understand what it's going to be like. You're not the sole investigator from beginning to end. The work is very detailed and sometimes can get overwhelming, because it is a lot of paperwork and protocols and making sure you're doing things right.

Also, you’ll have to testify in court and give talks and presentations. You’re not just stuck in a lab. It’s a great profession; it's always interesting and there's always going to be something to do.

What does LA mean to you?
LA to me means, family, comfort, good weather. It's just a nice relaxing place to live, I think. I've lived in New York and San Francisco, and I think there's just a lot of hustle and bustle. That was really fun for my 20s, but I think LA just feels like home. It's a place to not always think, "What am I going to do next?" My Sunday is just relaxing.


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Photography by Magdalena Wielopolski ©

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